Choke input filter LF noise - Page 3 - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 6th June 2011, 07:25 PM   #21
piano3 is offline piano3  United Kingdom
diyAudio Member
 
Join Date: Aug 2010
Location: London,UK
nicely put!!
  Reply With Quote
Old 6th June 2011, 07:39 PM   #22
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
Series resistance will damp any resonance, and improve the low pass filtering action especially at very low frequencies where the choke is giving up. Provided the resonance is reasonably well-damped, you then need to think about either more filtering or active solutions like regulators.
  Reply With Quote
Old 6th June 2011, 07:42 PM   #23
diyAudio Member
 
Rundmaus's Avatar
 
Join Date: Aug 2005
The described filter chain in my case suffers from a slightly high Q-factor, but as long as I do not encounter problems with it, I am not willing to burn precious B+ voltage in additional series resistors...
  Reply With Quote
Old 6th June 2011, 07:43 PM   #24
piano3 is offline piano3  United Kingdom
diyAudio Member
 
Join Date: Aug 2010
Location: London,UK
Thanks DF, you have brought up several points I have not considered and with your usual clarity.
  Reply With Quote
Old 6th June 2011, 07:46 PM   #25
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
You can also damp the resonance with a snubber (C+R) to ground. No extra voltage drop that way. Effectively the snubber is an AC-only resistance. We usually think of snubbers as working at RF frequencies, but the principle applies to subsonic too. You just need much bigger caps!
  Reply With Quote
Old 6th June 2011, 07:48 PM   #26
diyAudio Member
 
Rundmaus's Avatar
 
Join Date: Aug 2005
Can you go into more detail on that?

*interested*
  Reply With Quote
Old 6th June 2011, 07:57 PM   #27
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
I don't know the design equations for a snubber off the top of my head, but I'm sure Google will help. Essentially the resistor needs to be the right size to damp the resonance, roughly making up what is lacking from the load. Too big and it won't damp enough. Too small and the PSU will be slow to recover from demand peaks. Then the capacitor in series with it needs to be big enough to ensure that around the resonance frequency the resistor is 'seen' by the resonance. Too big and you almost have an extra smoother; too small and it won't do much damping.

You can either find the equations, or play with it in Spice. Or do both. That is about the extent of my knowledge - I would have to start doing algebra to get any further and I'm sure someone will have already done it somewhere.
  Reply With Quote
Old 6th June 2011, 10:51 PM   #28
diyAudio Member
 
trobbins's Avatar
 
Join Date: Feb 2009
Location: Melbourne, Oz
You may want to consider the topic from a few different angles.

Any low frequency noise getting through the power supply filtering will get attenuated through an OT, and also attenuated on its way to any preamp stage assuming there is resistive dropping to those stages. Assuming the magnitude of the <f(mains) noise is less than your mains ripple, then it's importance to amp performance is similarly proportionally less important.

If the low frequency noise is mainly in the form of disturbances, and not periodic, then each disturbance introduces a form of step disturbance to the LC filter and hence higher frequency components will be introduced. If the Q of the LC, or CLC, sections is >1 then any disturbance frequency component within the Q peak of the filter will be amplified in level, and depending on levels and Q could become significant at the output of the power supply.

Managing the Q of the filter can also be done using parallel R - which is a common technique for dampening higher frequency self-resonances within the choke - it does somewhat reduce the filter attenuation at the mains ripple frequencies. Even more exotic parallel R-zener(back-to-back) can be used for managing large signal disturbances, but I doubt you are experiencing low frequency disturbances with a magnitude across the choke that is much larger than mains ripple.

Imho, applying RC or resonant trap sections to the LC filter could be an onerous path to take, and possibly only applicable if you have a significant repetitive specific noise issue that can benefit from a specific tailoring of the LC filter response.

Ciao, Tim
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
choke input power supply filter audionut Pass Labs 55 20th May 2013 08:17 PM
Choke Input Filter on Class A PS john65b Power Supplies 2 20th April 2009 09:48 AM
Choke, filter for white noise grandcanuck Analog Line Level 0 10th September 2008 04:20 PM
Choke Input Filter. G Tubes / Valves 8 11th February 2008 08:57 PM
SOZ Choke input filter? gnomus Pass Labs 48 14th May 2004 06:41 PM


New To Site? Need Help?

All times are GMT. The time now is 11:10 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2